Field of the Invention
The present invention relates to an acoustic tube and a narrow directional microphone using the acoustic tube, and more particularly relates to an acoustic tube that can prevent intrusion of water and a narrow directional microphone using the acoustic tube.
Description of the Related Art
In narrow directional microphones having an acoustic tube, the acoustic tube is joined to a front portion of a microphone unit, and the joint portion is sealed so as to prevent sound waves penetrating into an inside through the joint portion. Such a configuration realizes narrow directivity but causes to increase an influence of wind noise, and an influence of proximity effect when a sound source is close.
To solve the problem, the applicant of the present application discloses, in Japanese Patent No. 2562295B2, a configuration in which a plurality of openings (sound wave introduction ports) is provided in a tube wall of an acoustic tube (made of aluminum) that accommodates a microphone unit, and an acoustic resistor (fabric, non-woven fabric, or the like) is affixed to portions outside the openings.
According to the configuration disclosed in the above document, influence of the wind noise and the proximity effect can be reduced compared with the conventional narrow directional microphones.
By the way, the narrow directional microphones as described above are often used outdoors because the microphones can eliminate ambient noise and can collect sounds of a target sound source.
However, as disclosed in the above document, the structure having the plurality of openings in the tube wall of the acoustic tube has a problem that, if the acoustic tube gets wet because of rain, for example, water infiltrates into the acoustic resistance material affixed to the openings of the tube wall, and the water penetrates into an interior of the acoustic tube, which may be a cause of breakdown of the microphone unit.